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    <script>
        /**
         *  var 的变量名重复了，后面重复的var 直接忽略
         *  function 函数名重复了，后面的函数会覆盖前面的函数
         * 
         */
        console.log(a);
        var a = 1;
        var a = 2;
        var a = 3;
        console.log(a);
        fn();
        function fn(){
            console.log('fn1');
        }   
        function fn(){
            console.log('fn2');
        }
        fn();
    </script>
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